The present invention relates generally to medical fluid systems and more particularly to the testing and priming of such systems.
It is known in peritoneal dialysis systems to perform integrity tests that attempt to verify that the numerous fluid valves in a disposable cassette do not leak, that leaks do not occur between multiple pump chambers in the cassette, that leaks do not occur across fluid pathways, and that an isolation occluder, which is intended to stop liquid flow in fluid lines connected to the cassette in the event of a system malfunction, is performing that procedure properly. In one known wet leak test described in U.S. Pat. No. 5,350,357, a disposable cassette is loaded into a peritoneal dialysis cycler and the solution bags are connected. The test consists of the following steps:
(i) a negative pressure decay test of the fluid valve diaphragms is performed;
(ii) a positive pressure decay test of the fluid valve diaphragms is performed;
(iii) a positive pressure decay test is performed on the first pump chamber, while a negative pressure decay test is performed on the second pump chamber;
(iv) a negative pressure decay test is performed on the first pump chamber, while a positive pressure decay test is performed on the second pump chamber; after which
(v) both pump chambers are filled with a measured volume of fluid, all fluid valves are opened and the occluder is closed, positive pressure is applied to both pump chambers for a period of time, after which the volume of fluid in each pump chamber is measured again to determine if any fluid has leaked across the occluder.
As indicated, the above testing procedure is performed after solution bags are connected to the peritoneal dialysis system. If integrity of the cassette or tubing is faulty, the sterility of the solution bags becomes compromised. In such a case, both the disposable cassette and solution bags have to be discarded. Additionally, it is possible that liquid from the solution bags can be sucked into the machine's pneumatic system, causing the pneumatic system of the machine to malfunction.
Wet tests are also susceptible to false triggers. In particular, cold solution used in the test causes many false disposable integrity test alarms each year because the tests fail when an occluder, which is supposed to clamp off all fluid lines, does not properly crimp or seal the tubing lines. When the solution is cold, it cools the set tubing to a lower temperature than the tubing would be if placed only in room air. Colder tubing is harder to occlude, allowing fluid in some cases to leak past the occluder and cause the test to fail. Once a dialysis therapy starts, the fluid passing through the tubing is warmed to about 37° C., enabling the occluder to perform satisfactorily.
It is therefore desirable to have an integrity test that is performed before the solution bags are attached to the therapy machine and to eliminate the use of cold solution to prevent false triggers.
A “dry” test is described briefly in U.S. Pat. No. 6,302,653. The description is based in part upon the “dry test” implemented in the Baxter HomeChoice® cycler in December of 1998. The actual test implemented in the HomeChoice® cycler consists of four steps, the first of which occurs before the solution bags are connected. The next three steps require the solution bags to be connected but do not require fluid to be pulled from the bags into the machine. FIGS. 1 to 4 illustrate the areas of a fluid cassette tested by the individual steps of the known “dry” test. While the above “dry” test eliminates the problem of fluid potentially leaking into the pneumatics of the machine, the test does not prevent the sterility of the bags from being compromised potentially upon a leak and thus from being discarded if the integrity of the disposable cassette is compromised.
Moreover, dry testing with air is believed to be more sensitive than the wet test, which uses dialysis fluid. It is therefore also desirable to have an integrity test that uses air for sensitivity reasons as well as for the reasons stated above.
While integrity testing poses one problem to manufacturers of medical fluid machines, another common problem is the priming of the fluid system within those machines. In many instances, air must be purged from one or more tubes for safety purposes. For example, in the realm of dialysis, it is imperative to purge air from the system, so that the patient's peritoneum or veins and arteries receive dialysis fluid that is free of air. Consequently, automated dialysis machines have been provided heretofore with priming systems. In peritoneal dialysis, the object of priming is to push fluid to the very end of the line, where the patient connector that connects to the patient's transfer set is located, while not priming fluid past the connector, allowing fluid to spill out of the system.
Typically, dialysis machines have used gravity to prime. Known gravity primed systems have a number of drawbacks. First, some priming systems are designed for specifically sized bags. If other sized bags are used, the priming system does not work properly. Second, it happens in many systems that at the beginning of priming, a mixture of air and fluid can be present in the patient line near its proximal end close to a disposable cartridge or cassette. Fluid sometimes collects in the cassette due to the installation and/or integrity testing of same. Such fluid collection can cause air gaps between that fluid and the incoming priming solution. The air gaps can impede and sometimes prevent gravity priming Indeed, many procedural guides include a step of tapping a portion of the patient line when the line does not appear to be priming properly. That tapping is meant to dislodge any air bubbles that are trapped in the fluid line.
A third problem that occurs relatively often in priming is that the patient forgets to remove the clamp on the patient line prior to priming that line. That clamped line will not allow the line to prime properly. An alarm is needed to inform the patient specifically that the patient needs to remove the clamp from the patient line before proceeding with the remainder of therapy. Fourth, if vented tip protectors are provided at the end of the patient line, the vented tip protectors may not vent properly and impede priming. An alarm is again needed to inform the patient that the line has not primed properly. Fifth, cost is always a factor. Besides providing a priming apparatus and method that overcomes the above problems, it is also desirable to use existing components to perform the priming, if possible, to avoid having to add additional components and additional costs.
Another concern for medical fluid systems and in particular automated peritoneal dialysis (“APD”) systems is ensuring that solution bags are placed at a height relative to the machine that is suitable for the machine to operate within designated parameters. The height of solution bags, such as dialysate bags, lactate bags and/or dextrose bags, needs to be monitored to ensure that the proper amount of fluid will be pumped to the patient during therapy and that the correct amount and proportion of additives are infused. Two patents discussing bag position determination are U.S. Pat. Nos. 6,497,676 and 6,503,062.